1. Field of the Invention
In one aspect, the invention provides new ceramic resistive igniter elements that comprise an inner first conductive zone, a resistive hot zone, and an outer second conductive zone, all in electrical sequence. In preferred igniters, at least a substantial portion of the first conductive zone does not contact a ceramic insulator. Preferred igniters of the invention are substantially rod-shaped (e.g. rounded cross-sectional shape such as substantially circular cross-sectional area) and can exhibit good mechanical integrity and time-to-temperature properties.
2. Background
Ceramic materials have enjoyed great success as igniters in e.g. gas-fired furnaces, stoves and clothes dryers. Ceramic igniter production includes constructing an electrical circuit through a ceramic component a portion of which is highly resistive and rises in temperature when electrified by a wire lead. See, for instance, U.S. Pat. Nos. 6,028,292; 5,801,361; 5,405,237; and 5,191,508.
Typical igniters have been generally rectangular-shaped elements with a highly resistive “hot zone” at the igniter tip with one or more conductive “cold zones” providing to the hot zone from the opposing igniter end. One currently available igniter, the Mini-Igniter, available from Norton Igniter Products of Milford, N.H., is designed for 12 volt through 120 volt applications and has a composition comprising aluminum nitride (“AIN”), molybdenum disilicide (“MoSi2”), and silicon carbide (“SiC”).
A variety of performance properties are required of ceramic igniter systems, including high speed or fast time-to-temperature (i.e. time to heat from room temperature to design temperature for ignition) and sufficient robustness to operate for extended periods without replacement. Many conventional igniters, however, do not consistently meet such requirements.
Spark ignition systems are an alternative approach to ceramic igniters. See, for instance, U.S. Pat. No. 5,911,572, for a particular spark igniter said to be useful for ignition of a gas cooking burner. One favorable performance property generally exhibited by a spark ignition is rapid ignition. That is, upon activation, a spark igniter can very rapidly ignite gas or other fuel source.
In certain applications, rapid ignition can be critical. For instance, so-called “instantaneous” water heaters are gaining increased popularity. See, generally, U.S. Pat. Nos. 6,167,845; 5,322,216; and 5,438,642. Rather than storing a fixed volume of heated water, these systems will heat water essentially immediately upon opening of a water line, e.g. a user turning a faucet to the open position. Thus, essentially immediate heating is required upon opening of the water to deliver heated water substantially simultaneously with the water being turned “on”. Such instantaneous water heating systems have generally utilized spark igniters. At least many current ceramic igniters have provided too slow time-to-temperature performance for commercial use in extremely rapid ignition applications such as required with instantaneous water heaters.
Current ceramic igniters also have suffered from breakage during use, particularly in environments where impacts may be sustained such as igniters used for gas cooktops and the like.
It thus would be desirable to have new ignition systems. It would be particularly desirable to have new ceramic igniters with enhanced time-to-temperature properties. It also would be desirable to have new igniters that have good mechanical integrity.